The present invention relates to a novel and useful device for primarily detecting mammalian keratoconjunctivitis sicca.
Keratoconjunctivitis sicca (KCS) or "dry eye" is an ophthalmic condition defined by an insufficiency or imbalance of one or more of the ocular fluid components of an eye. Such imbalance may involve aqueous tear fluid, conjunctival mucin, and/or tear fluid lipid. KCS frequently threatens ocular anatomic integrity, often causing conjunctival and corneal erosion. "Dry eye" is a finding in about 25% of Sjogren's syndrome, which most often occurs in women past the age of 45 years. Sjogren's syndrome often detrimentally affects the immune system of the body; thus early detection and treatment is important. It has been estimated that several million persons in the United States alone are affected by KCS. 90% of such KCS cases are due to Sjogren's syndrome. KCS also commonly afflicts several canine species.
A moderate case of KCS is normally first noted clinically as ocular surface "burning", itching, prickly corneal pain, altered vision, accumulation of mucus threads, occasional overflow of reflex tears, and other forms of ocular surface discomfort due to the noted aberrance of tear fluid components.
The Schirmer tear production test is now one of the two mainstay diagnostic tests for KCS, Such test consists of measuring the length of wetting of a standardized filtered paper strip which is notched and folded over the eyelid margin, into the inferior fornix, and may be performed with or without anesthetic. The Schirmer test is cumbersome and time consuming, as well as inaccurate. Reproducibility of the Schirmer test, in the hands of the average practitioner, varies between 25% and 50%.
Rose bengal ocular surface staining is the other mainstay test employed to detect KCS. This test, which is somewhat time consuming, stains devitalized cells and mucin in the tear film. Rose bengal staining, although moderately accurate, is not completely diagnostic of KCS, since it does not detect "early" cases, which represent a significant fraction of KCS occurence. Rose bengal staining does effectively uncover "later" stages of KCS which are termed moderate to severe, but such test does not grade the fundamental tear osmolality defect.
The tear "break up time" test may also be used to detect KCS. In such a test, a fluorescein strip is used to initially stain the tear film and the time to first corneal tear film breakup is noted under slit lamp biomicroscope observation. Even with repeat measurements, the accuracy is highly variable in this test.
Reference is made to U.S. Pat. No. 4,269,197 to Gilbard in which a micropipette is employed to take human tear samples for measurement of tear osmolarity, generally by freezing point depression determination. Such a meticulous, time consuming test is prohibitive in a routine clinical setting and requires a relatively long time period between obtaining a tear fluid sample and analysis of the same. Also, most eye care practitioners do not possess the freezing point depression apparatus required for this test. Gilbard et al in an article "Osmolality of Tear Microvolumes In Keratoconjunctivitis Sicca" Arch Ophthalmol. 1978,96, 677-81, correlated measurement of tear osmolarity/osmolality to the existence and clinical severity of KCS in patients.
Lingual and vaginal muscosal surface conductance measurements have been taken by in vivo tissue contacting devices to acertain the time of mammalian ovulation. Conductance in the vaginal mucus have been observed and linked largely to sodium and chloride ionic activity, therein. An article by Aboul-ela et al entitled "Relationships Between Intravaginal Electrical Resistance, Cervicovaginal Mucus Characteristics and Blood Progesterone and LH" describes measurements of intravaginal electrical resistance made on Hereford-Friesian heifers. In addition, a mucus epithelial conductance-based ovulation predictor or monitor is manufactured by Zetek Inc. of Aurora, Colo. under the name "Cue" for human use.
Skin electrical impedance has been extensively gauged using aqueous gel coatings and contact electrodes in conjunction with electrocardiogram measurements. For example, an article entitled "A Model For Skin-Electrode Impedance" by Swanson et al, describes such measurements.
Also, ion specific electrodes for solutions have been developed. For example, Fisher Scientific Company of Pittsburg, PA. describes such electrodes under the designation "pH/pX". Further, ion-selective membranes are defined in the "Encyclopedia of Medical Devices and Instrumentation", Edited by Webster, J. for use in clinical and medical fields.
There are no known devices or methods for measuring the electrical or specific ion activity of the ocular fluid in its natural condition of coating the ocular surface in vivo.
The accurate measurement of human ocular tear fluid osmolarity with a simple, rapid method and apparatus would be an important advance in the medical field.